1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording head and particular configuration of laser diode unit.
2. Description of the Related Art
Recently in the magnetic recording apparatus which representative the magnetic disk apparatus, the improvement performance of the magnetic recording medium and the thin film magnetic head is required with high density recording. Regarding the thin film magnetic head, the composite-type thin film magnetic head that is stacked with reproducing head with the magnetic resistive effect element for reading and recording head with induction-type electromagnetic transducer element for writing, have been widely used.
The magnetic recording medium is the discontinuous medium on which the magnetic nanoparticles aggregate. Each magnetic nanoparticle has the single magnetic domain structure. Each recording bit on the magnetic recording medium is configured by plural magnetic nanoparticles. To increase the recording density, unevenness at a boundary between neighboring bits must be decreased. For the purpose, it is necessary to make the magnetic nano particles small. On the other hand as for the small magnetic nanoparticle, in other words the small magnetic nanoparticle of the small volume, heat stability of the magnetization decreases. To solve this problem it is effective to increase the anisotropic energy of the magnetic nanoparticle. However, the big anisotropic energy of the magnetic nanoparticle increases the coercive force of the magnetic recording medium and makes recording the information with the conventional magnetic head difficult.
As the method to solve this problem, a so-called thermally assisted magnetic recording is proposed. In this method the magnetic recording medium with large coercive force can be used. On recording the information, by simultaneously applying the magnetic field and heat to the part of the magnetic recording medium which is recorded the information, the temperature of the part is increased. Thereby the information is recorded by magnetic field in the part of which its coercive force is reduced. Hereinafter, the magnetic head used in the thermally assisted magnetic recording is named the thermally assisted magnetic recording head.
In the thermally assisted magnetic recording, the laser light source is generally used as a means to apply heat in the magnetic recording medium. Laser light is converted into near-field light and near-field light heats the magnetic recording medium. Near-field light is a type of electromagnetic field formed around material, and does not have limitation of diffraction limit from the light wavelength. By irradiating light of which wavelength is harmonious to the microstructure body, the near-field light depending on the scale of a microstructure body is formed. As a result, it is possible to narrow light to the very small domain of the dozens of nanometers.
JP. Patent Publication No. 2001-255254 discloses the thermally assisted magnetic recording head using near-field light probe formed of metal piece that is so-called plasmon antenna. The plasmon antenna generates the near-field light from the plasmon excited by light. But because the greater part of the energy of the irradiated light is reflected in the surface or converted into heat energy, the conversion efficiency is low. Because the size of the plasmon antenna is set in lower than wavelength of the light, the volume is small and temperature increase caused with heat generation is very intense. Therefore, the plasmon antenna is prone to produce diffusion, cohesion, fusion and does not have enough reliability.
U.S. Patent Publication No. 2010/0,103,553 discloses the thermally assisted magnetic recording head using the near-field light generator. The near-field light generator is positioned apart from the waveguide and is coupled with the waveguide in surface plasmon polariton mode. That is to say, the total reflection of light propagating on the interface of the waveguide generates the evanescent light penetrating from the interface. The surface plasmon is excited on the surface of the near-field light generator by coupling this evanescent light with collective oscillation of the charge on the near-field light generator, namely the surface plasmon. The surface plasmon excited on the near-field light generator is propagated into the end part located on the air bearing surface S through the propagation edge and generates the near-field light at the end part. Because the near-field light generator is not irradiated with the light propagating in the waveguide, the near-field light generator is prevented from being excessively heated. The wavelength of the laser light that is entered to the wavelength is within 375 nm to 1,700 nm.
In the near-field light generator which uses the coupling of surface evanescent light and surface Plasmon, an excessive temperature increase is not likely to occur. But to realize long-term reliability which is required in the magnetic recording apparatus or the magnetic head, further improvement is demanded. The thermally assisted magnetic recording head is more disadvantageous in a cost view than the conventional magnetic recording head without the heating means to a magnetic recording medium.
This invention is intended to provide a thermally assisted magnetic recording head in which the excessive temperature increase of the near-field light generator is not likely to occur and the influence on cost is suppressed.